Optical sensing system for detecting and storing the position of a point source target

ABSTRACT

The position of a point source target in a field of view is simultaneously focused onto a plurality of sensing units by means of a multifaceted lens. Each of the sensing units has a photosensitive area which is divided into a pair of equal area sensing elements which are arranged in either horizontal or vertical finger patterns. The finger patterns are arranged in a binary coded fashion and at any particular time one or the other of the elements of each unit generates an output in response to the optical target, the combination of such outputs being indicative of the position of the target. The output of the optical sensing units are fed to digital registers which develop a binary coded signal indicative of the target position for utilization in a readout device.

2,081,936 6/1937 Keenan Inventor Stanley C. Requa Northridge, Calil.

Appl. No. 789,285

Filed Jan. 6, 1969 Patented Aug. 31 1971 Assignee Northrop CorporationBeverly Hills, Calif.

OPTICAL SENSING SYSTEM FOR DETECTING AND STORING THE POSITION OF A POINTSOURCE TARGET 4/1969 Harris 340/173 3,480,919 11/1969 Jensen... 340/1733,488,636 1/1970 Dyck 340/l73 Primary Examiner-Terrell W. FearsAttorney-Sokolski & Wohlgemuth ABSTRACT: The position of a point sourcetarget in a field of view is simultaneously focused onto a plurality ofsensing units by means of a multifaceted lens. Each of the sensing unitshas a photosensitive area which is divided into a pair of equal areasensing elements which are arranged in either horizontal or verticalfinger patterns. The finger patterns are arranged in a binary codedfashion and at any particular time one or the other of the elements ofeach unit generates an output in response to the optical target, thecombination of such outputs being indicative of the position of thetarget. The output of the Optical sensing units are fed to digitalregisters which develop a binary coded signal indicative of the targetposition for utilization in a readout device.

PATENTED AUBBI 197i SHEET 1 UF 4 INVENTOR.

TANLEY C. REQUA OLSKI 8| WOHLGEMUTH I 0 304 O BOa PATENTED M1831 Ian3,602,903

FIG. 3A INVENTOR.

STANLEY C. REQUA SOKOLSKI B: WOHLGE MUTH ATTORNEYS PAIENIEI] AUG3I IEIII3,602,903

SHEET 0F 4 VERTICAL STORAGE d- REGISTER FMCESSER G I'DRIZONTAL STORAGEREGISTER PFUZESSER READOUT DEVICE TO REGISTER I NVENTOR.

STANLEY C. REQUA SOKOLSKI 8 WOHLGEMUTH ATTORNEYS OPTICAL SENSING SYSTEMFOR DETECTING AND STORING THE POSITION OF A POINT SOURCE TARGET.

' systems and infrared detection in fire control systems. Active targetdetection systems utilizing a laser beam to illuminate the target alsoinvolve point source'detection.

Point source detection systems of the prior art generally involve analogimplementations whereby the optical sensor is first slewed into positionwhere it is close to alignment with the target and at which nearlyaligned position it is capable of developing a control signal whichoperates a servo loop to lock the sensor onto the target and maintain itin such lockon position. While the analog control signal is fullycapable of accurately operating a servo loop," it generally is notprecisely proportional to the deviation of the target from thesensor'bore axis at all times due to inherent nonlinearities involvedin-many analog implementations. Further, such target acquisition systemsof the prior art are generally not capable of producing a signalindicative'of the target position over any but a narrow field of view.Further, many systems presently utilized for navigation and fire controlapplications, with which target acquisition of the contemplated typesare involved, utilize digital implementations and thus have a certaindegree of incompatibility with the aforementioned analogimplementations. I I

The system of this invention overcomes the above indicated shortcomingsof the prior art by providing a point source optical target detectorwhich directly generates a digital readout which is in accordance withthe position of the target in an op- I tical field of view Continualdigital readout is provided indicating precisely where the target iswithin such field of view, such precision being achieved by virtue of aposition matrix definedv by the sensors. The precision is limited onlyby the resolution of the matrix and not by nonlinearity factors asencountered in analog systems. This end result is achieved without theutilization of a scanner device and can be imple merited either in apassive or an active detection system.

It is therefore the principal object of this invention to provideanimproved optical point source target sensor which provides a digitaloutput in accordance with the position of the target in a field of view.

The invention will now be described in connection with the drawings, ofwhich:

FIG. 1 is a perspective view illustrating one embodiment of theinvention in its assembled form,

FIG. 2 is an exploded view ofthe embodiment of FIG. 1,

FIGS. 3a and 3b are schematic views illustrating sensor units ofapreferred embodiment of the invention, I

FIG. 4 is a schematic view illustrating typical targets within aposition matrix of the field of view of the embodiment of FIG. 1, I

FIG. 5 is a schematic view illustrating the interconnections between thesensor units and storage registers of the embodiment of FIG. I, and

FIG. 6 is a schematic view illustrating the development ofa readoutsignal from a sensor which may be used in the device of the invention.

Briefly described, the device of the invention comprises a multifacetedlens which focuses an image of a point source target onto a plurality ofoptical sensor units. Each sensor unit has a flat photosensitive areawhich is divided equally between a pair of sensor elements. The sensorelements are arranged in binary coded finger patterns. The outputs ofeach pair of sensor elements are fed to the storage elements of adigital storage register, each such storage element being actuated inaccordance with the binary optical excitation of the associated sensorunit. Thus, the storage register has a binary coded signal'therein whichis indicative of the position of the target in the matrix of the fieldof view, this binary coded signal being fed to a readout device.

Referring now to. FIGS. 1 and 2, one embodiment of the device of theinvention is perspectively illustrated. Mounted in casing 11 is amultifaceted or fly-eye lens 12 which focuses an image of target 10 oneach of the'sensor units 14-19 of sensor 13. Thus, lens. elementsl2a-12f simultaneously focus images of target 14 at correspondingpositions on sensor units 14-19respectively. As to be explained morefully further on in the specification, sensor units 14-19 each comprisesa 'pair. of photosensitive elements which are divided in binary fashionso that each sen- -sor'element covers half of the area of its associatedunit. Sensor units 14, 16 and 18 have theirelements arranged in verticalfinger patterns, while sensor units 15, 17 and 19 have sensor elementsarranged in horizontal finger patterns. Tl-le outputs of sensor units14, 16 and 18 are each fed to aseparate storage unit of storage register21 which is mounted on board 23 while the outputs of sensor units 15, 17and 19 are each fed to register units of a similar storage register-'20mounted on board 23.

Referring now to FIGS. 3a, 3b and 4, the operation of the invention willnow be described. Sensor units 14-19 are each divided into equalphotosensitive sensing elements 14a, 14b-19a 19b respectively. Thephotosensitive areas, as to be explained fully further on in thespecification, may be formed by silicon wafers. It is to be noted thatthe elements of each unit are separated from each other so that they arecapable of forming independent electrical current paths. The sensorelements l4a-19 and l4b-l9b are arranged in binary coded fingerpatterns, the elements of sensor units 14,16 and 18 being oriented in afirst direction which may be vertical, while the elements ofsensor-units 15 17 and 19 are oriented normal to those of units 14, 16and 18 in a direction which may be horizontal. The resolution obtainablewith six sensor units as shown in the illustrative embodiment is asdefined by an 8X8 position matrix, as shown in FIG. 4. That is to say,each of the matrix squares represents the definition orresolutioncapability'of the system in sensing a target. It is to benoted that the particular six-unit sensor system shown is onlyillustrative and a higher resolution system can readily be constructedutilizing the same principles as described herein but with additionalsensor units The matrix resolution obtainable with any particular numberof binary sensor units of the type described can be determined byraising2 to a 'powerwhich is equal to" the number of sensor unitsdivided by 2. Thus, for example, the resolution of a 16Xl6 matrix can beobtained with 8 sensor units and a 128x128 resolution matrix with 14sensor units. Thus, it can be seen that very high resolution can beobtained with a relatively small number of sensor units.

Referring now to FIGS. 3a and 4, the sensing of a target signal 30awhich appears at the matrix position 3,6 in the field of view is shown.As shown in FIGS. 2 and 30, target signal 30a is focused by themultifaceted lens 12 onto sensor elements 14a, 16b, 18b, 15b, 17b, and19b. As to be explained more fully in connection with FIG. 5, theoptical signal 30a causes the sensing element on which it impinges togenerate a signal to an associated register unit, thus providing abinary coded signal uniquely representing the matrix position 3,6.

Referring now to FIGS. 3b and 4, a second example, i.e., for a targetsignal 30b in position 8,3 in the matrix is shown. It is to be notedthat only a single point source target can be read at a time, and targetsignals 30a and 30b could not be read out of the system simultaneously.As shown in FIG. 3b, the target 30b energizes sensor units 14b, 16a,18a, 15a, 17b, and 19b, to provide a unique digital output for readoutfrom a digital storage register which defines the position of target 30bon the matrix at 8,3.

Referring now to FIG. 5, the sensor elements of vertical sen sor units14, 16 and 18 are each fed to a separate flip-flop storage unit 40-42respectively of vertical storage register and processor 21. The "asensing element of each pair is fed to one of the flip-flop stages ofeach flip-flop unit, while the b sensing element is fed to the otherflip-flop stage of this same unit. Thus, each flip-flop unit is set inone or the other of its binary conditions, depending upon which of thesensing elements of the pair is activated at any time.

Similarly, the sensing elements of horizontal sensor units l5, l7, and19 are fed to flip-flop storage units 43, 44 and 45 respectively ofhorizontal storage register and processor 20, such flip-flop units beingactuated in the same manner as just described for the vertical units.

it thus can be seen that the flip-flop storage units 4045 will beactuated in binary form in accordance with the actuation of the pairsofsensing elements.

Listing the condition of the a sensing unit first, and assuming theactuation of the flip-flop stages labeled a in FIG. 5 to represent aTRUE condition, the following is the truth table for targets 30a and3012, as indicated on the matrix of HO. 4 for each of the sensing units:

Sensor Units 14 l6l8l5 1719 I001 Ol 01 01 Ol 01 ll) l0 lOOl 0| Thevertical and horizontal storage registers and 21 are actuated asindicated in the above table, and the unique binary coded signals foreach position on the matrix are appropriately processed and fed toreadout device 39 for utilization in either tracking the target,providing display information therefor, or for other applicationrequirements.

Referring now additionally to FIG. 6, the construction of a sensor unitwhich may be utilized in the device of the invention is illustrated. Theparticular device illustrated in FIG. 6 is a reverse bias Schottkybarrier photodiode and is one of several types of devices that may beutilized for the sensor units.

The sensor units comprise an N-type of silicon wafer which is attachedto a metallic backing 51 as, for example, by alloying. A single commonbacking plate 51 may be utilized for all of the sensing units, as shownin FIG. 5, and provides a common connection therebetween. Plate 51 maybe of a highly conductive material such as copper. Finger pattern sensorelements are delineated by semitransparent gold layers 53a and 53b whichare vacuum deposited on silicon wafers 50. The gold conductors 53a and5317 are separated from each other and deposited in the forms indicatedin HO. 5 to provide the finger pattern sensing elements 14a-19a and14b-l9b. The sensing elements formed by the vacuum deposited fingerpatterns, the silicon wafers and the conductive backing are reversebiased by means of direct current power source 57.

When a beam of light is focused on a portion of the surface of a siliconwafer 50 through the semitransparent gold layer 53a or 53b thereabove. acurrent will flow from the surface of the wafer to the gold layerportion 530 or 53b immediately overlaying it, such current flowingthrough an associated one of resistors 590 or 59b as the case may be,thereby providing output signals to the register in accordance with theportions of the sensing units that have received light excitation. Thus,for example, if a light beam is focused onto wafer 50 in the areacovered by gold layer 53a, a current will be caused to flow throughresistor 59a, providing a 1" output to the appropriate register unit,the other gold overlay section 53b having no significant current flowthrough resistor 59b. Conversely, aspot of light on the area of thewafer by layer 53b will result in a 0" output to the register.

it is to be noted that this is but one of several fabrication techniquesthat can be used for the photoconductive sensors. Photosensitive devicesproduced by thin film or diffusion techni ues may also be utilized. vThe evice of this invention thus provides means for providingcontinuousinformation in digital form as to the position of a point source opticaltarget.

I claim:

1. A system for generating a digital readout signal in accordance withthe position of an optical point source target, comprising:

a plurality of sensor units, each of said sensor units comprising a pairof light sensitive sensor elements arranged in binary coded fingerpatterns,

multifaceted lens means for simultaneously focusing an image of thepoint source target on one or the other of the sensor elements of eachof said sensor units, and

digital storage register means for receiving the outputs of said sensorunits and developing a binary coded signal uniquely indicative of theposition of said target. I

2. The device of claim 1 wherein said multifaceted lens means comprisesa plurality of similar. lens elements for focusing an image of thetarget at corresponding portions of each of said sensor units.

3. The device of claim I wherein one half of said sensor units includesensor elements having finger patterns running in a first direction, andthe other half of said sensor units have sensor elements with fingerpatterns running in a direction normal to said first direction.

4. The device as in claim 1 wherein each of said sensor units comprisesa conductive backing, a silicon wafer attached to said backing, andmetallic layers deposited on said wafer to form said finger patterns.

5. The device of claim 4 and further including power source means forback biasing said wafer and a load resistor connected between said powersource means and each of said sensor elements, a voltage being developedacross each of said load resistors when the sensor element connectedthereto has an image of the target focused thereon.

6. The device of claim 3 wherein said storage register means includes afirst digital register for receiving the outputs of said one half ofsensor units and a second digital register for receiving the outputs ofsaid other half of said sensor units.

7. In an optical sensing system for detecting the position of a pointsource target,

a plurality of sensor units, each of said sensor units comprising aphotosensitive area divided equally between a pair of sensor elements, I

means for focusing an image of said target onto a corresponding portionof each of said sensor units, and

digital storage register means for generating a binary coded signal inaccordance with the outputs of said sensor units, said digital storageregister means comprising a binary storage element connected to receivethe sensor element outputs of each of said sensor units.

8. The system of claim 7 wherein said sensor elements are arranged inbinary coded finger patterns, the elements of each pair being similar inconfiguration to each other.

9. The system as recited in claim 7 wherein said focusing meanscomprises a multifaceted lens.

1. A system for generating a digital readout signal in accordance withthe position of an optical point source target, comprising: a pluralityof sensor units, each of said sensor units comprising a pair of lightsensitive sensor elements arranged in binary coded finger patterns,multifaceted lens means for simultaneously focusing an image of thepoint source target on one or the other of the sensor elements of eachof said sensor units, and digital storage register means for receivingthe outputs of said sensor units and developing a binary coded signaluniquely indicative of the position of said target.
 2. The device ofclaim 1 wherein said multifaceted lens means comprises a plurality ofsimilar lens elements for focusing an image of the target atcorresponding portions of each of said sensor units.
 3. The device ofclaim 1 wherein one half of said sensor units include sensor elementshaving finger patterns running in a first direction, and the other halfof said sensor units have sensor elements with finger patterns runningin a direction normal to said first direction.
 4. The device as in claim1 wherein each of said sensor units comprises a conductive backing, asilicon wafer attached to said backing, and metallic layers deposited onsaid wafer to form said finger patterns.
 5. The device of claim 4 andfurther including power source means for back biasing said wafer and aload resistor connected between said power source means and each of saidsensor elements, a voltage being developed across each of said loadresistors when the sensor element connected thereto has an image of thetarget focused thereon.
 6. The device of claim 3 wherein said storageregister means Includes a first digital register for receiving theoutputs of said one half of sensor units and a second digital registerfor receiving the outputs of said other half of said sensor units.
 7. Inan optical sensing system for detecting the position of a point sourcetarget, a plurality of sensor units, each of said sensor unitscomprising a photosensitive area divided equally between a pair ofsensor elements, means for focusing an image of said target onto acorresponding portion of each of said sensor units, and digital storageregister means for generating a binary coded signal in accordance withthe outputs of said sensor units, said digital storage register meanscomprising a binary storage element connected to receive the sensorelement outputs of each of said sensor units.
 8. The system of claim 7wherein said sensor elements are arranged in binary coded fingerpatterns, the elements of each pair being similar in configuration toeach other.
 9. The system as recited in claim 7 wherein said focusingmeans comprises a multifaceted lens.